CheckFortranSourceCompiles: Fix FAIL_REGEX documentation typo

Modules/CheckFortranSourceCompiles.cmake

@@ -13,7 +13,7 @@
 # ``<var>``
 #   Variable to store whether the source code compiled.
 #   Will be created as an internal cache variable.
-# ``<fail-regex>``
+# ``FAIL_REGEX <fail-regex>``
 #   Fail if test output matches this regex.
 #
 # The following variables may be set before calling this macro to modify